This application is the National Stage of International Application No. PCT/NL99/00152, filed Mar. 18, 1999, and published under PCT Article 21(2) in English, and claims priority to Netherlands Application No. 1008635, filed on Mar. 19, 1998. Each of the aforementioned related patent applications is herein incorporated by reference in its entirety.
1. Field of the Invention
The invention relates to a device for driving an object by vibration, in particular a pile or sheet piling to be driven into the ground or be removed therefrom, which device comprises a first eccentrically rotatable weight and a second eccentrically rotatable weight, which weights are interconnected by a phase shifter which is capable of adjusting the rotational position of the weights relative to each other. Vibration can be produced by having an eccentrically rotatable weight, that is, a rotatable mass whose centre of gravity does not lie on the axis of rotation, rotate about its axis. If said vibration comprises sufficient energy, it is possible to set an object vibrating therewith so as to drive said object into the ground by vibration. Although the present description describes the driving into the ground of objects, the device can also be used for removing objects from the ground.
By providing the device with two eccentrically rotatable-weights, the degree of vibration as well as the direction or directions of the vibration can be influenced by changing the relative rotational position of the two eccentric weights when said weights vibrate at the same speed. Consequently, the device is provided with a so-called phase shifter, which is disposed in the mechanical transmission which connects the two eccentric weights and which is capable of changing the relative rotational position of the two weights.
2. Description of the Related Art
A device of this kind is known from EP-A-0524056, wherein the phase shifter comprises two gears which are coaxially rotatable about a shaft, which gears occupy a fixed position relative to each other during normal operation of the vibrating device, but wherein the rotational position of one gear relative to the rotational position of the other gear can be slightly changed. Since each of the gears is in drivable contact with an eccentrically rotatable weight, the relative rotational position of the two weights can be adjusted by changing the rotational position of the two gears.
The phase shifter which is disclosed in EP-A-0524056 comprises a part which is connected with one gear and a part which is connected with the second gear, which parts are in part disposed radially apart, thus forming an annular cylinder space. An annular piston is present within said cylinder space, which piston abuts against each of said parts with a helical camway. The relative rotational position of the two gears can be changed by axial movement of the piston, which movement can be effected by means of fluid pressure.
The object of the invention is to provide a device of the kind as described above which is provided with a phase shifter, wherein said phase shifter can be controlled in a simple and adequate manner, and wherein said, phase shifter is reliable and of simple construction.
In order to accomplish that objective, the device is provided with a phase shifter comprising a differential which is provided with three interconnected, rotatable parts, wherein rotation of one part results in rotation of another part or of both other parts, the first part of which differential is in drivable contact with the first rotatable weight, and the second part of which is in drivable contact with the second rotatable weight, and wherein the rotational position of the third part determines the relative rotational position of the two rotatable weights. Such a mechanical differential is by itself a tried and tested part, of which there are a number of known embodiments, which are capable of functioning in a satisfactory, efficient and reliable manner. It has become apparent that such a mechanical differential can be used in a surprisingly simple manner in a phase shifter for a vibrating device.
Preferably, the first and the second weight form part of, respectively, a first and a second pair of eccentrically rotatable weights, wherein the two weights of each pair rotate in opposite directions, thus producing vibration substantially in one direction. The weights of each pair rotate at the same rotational speed, but in opposite directions, as a result of which said rectilinear vibration is obtained. By having two pairs of weights each produce rectilinear vibration, in both cases in the same direction, the vibration of one pair of weights can amplify or attenuate the vibration of the other pair of weights, depending on the rotational position of one pair of weights relative to the rotational position of the other pair of weights. All this is described in detail in the aforesaid EP-A-0524056.
Preferably, the three parts of the differential are coaxially rotatable relative to each other, and each of said parts comprises a gear which is in mesh with a gear of another part.
In one preferred embodiment, the first and the second part of the differential are coaxially rotatable conical gears whose teeth extend towards each other, and the third part is a coaxially rotatable carrier which carries one or more radially extending, relative to its axis of rotation, conical gears, wherein each of the latter conical gears is in mesh with both former conical gears. This is a type of differential which is also used in the rear axle of vehicles for driving the two rear wheels thereof.
Preferably, said carrier is fixedly mounted on a coaxial shaft, on which shaft said two former conical gears are mounted in a manner which allows coaxial rotation, and wherein the phase shift can be adjusted by rotation of the central coaxial shaft. This makes it possible to control the phase shift in an simple, mechanical manner.
In another preferred embodiment, said carrier is rotatably mounted on said central, coaxial shaft, and the carrier is fixed in the desired position by fixing means which are disposed outside the carrier, seen in radial direction. Said fixation may for example be carried out by moving a radially extending handle which is mounted on the carrier.
In the device according to the aforesaid EP-A-0524056, the two gears of the phase shifter rotate in the same direction. In the above-described device, the two gears of the phase shifter rotate in opposite directions. This does not complicate matters as regards the drive of the two pairs of eccentric wheels, since the direction in which the eccentrically rotatable wheels rotate has no influence on the generation of the rectilinear vibration.
In another preferred embodiment, the differential comprises planetary gearing comprising a sun gear, a satellite carrier and a planet gear, which are coaxially rotatable relative to each other. The advantage of a differential of this kind is that it has a limited dimension in axial direction. One drawback of such a planetary differential is the fact that when one of the parts is kept stationary, the two other parts will always rotate at different rotational speeds. When the two gears of the phase shifter have different diameters, however, this difference in rotational speed can be compensated in such a manner that the two gears rotate at the same peripheral velocity.
Preferably, the first part of the differential is the sun gear, the second part is the satellite carrier and the third part is the planet gear. The planet gear can be engaged from outside thereby so as to keep it in a stationary position, whilst one of the two gears of the phase shifter can be fixed on the central, coaxial shaft together with the sun gear.
In another preferred embodiment, the first part of the differential is the planet gear, the second part is the satellite carrier and the third part is the sun gear, which sun gear is fixedly mounted on the coaxial shaft, about which shaft the satellite carrier and the planet gear can rotate. The phase shift or the weights can thereby take place by rotation of the central shaft, in the same manner as described before.
The invention furthermore relates to a method for driving an object by vibration, in particular a pile or sheet piling to be driven into the ground, wherein a first eccentric weight and a second eccentric weight are rotated, wherein the rotational positions of the weights are adjusted relative to each other by means of a phase shifter, wherein said phase shifter comprises a differential which is provided with three interconnected, rotatable parts, wherein rotation of one part results in rotation of another part or of both other parts, and wherein said rotational position is adjusted by rotating part of said differential, whilst each of the other two parts is in drivable contact with an eccentric weight.
Further aspects, which can be used separately as well as in combination with each other, are described by means of two embodiments and defined in the claims.